Manufacture of nitrated cellulose from wood pulp



'sm-ges,1927., i '1,641,292

i v v. PLANCil-ioN4 MANUFACTURE oF NITRATED CELLULosE mn woon PULPA Filea'reb'. 27. 1925 to the fact that the sheets of wood pulp are Patented Sept. 6, 1927.

AUNITED sTA'lzs VICTOR PLANCHON, OF LYON, FRANCE. I

MANUFACTURE OF NITRATED CELLULOSE FROM WOOD PULP.

Application led February 27, 1925,v Serial No. 12,170, and in France February 29, 1924.

cording to the well-known nitration process.

Attempts have been made to substitute for cotton a less expensive raw material such, for instance, as wood pulp in sheets for example. but such attempts have hitherto proved fruitless and it is generally known that wood pulp is practically incapable of being nitrated by the known methods owing hydrolyzed and partly dissolved long before the nitration is completed.

In the present invention, only wood pulp in sheets is used to obtain nitrated cellulose.

The invention is characterized by the following points:

l. The usual nitration bath (a mixture of nitric acid and sulphuric acid) 1s used at a temperature always below 15 C., and the .sheets of wood pulp are immersed in the aforesaid bath for a sutcient period which depends on the temperature of such bath and which, consequently, varies with said temperature.

2. A method of manufacture is used which f is peculiar to the employment of wood pulp sheets for obtaining nitrated cellulose and which is altogether unsuitable for-the ordinary manufacture of nitrated cellulose from cotton, waste from spinning thin paper, etc.

In the annexed drawing:

Figure 1 is a perspective view, with parts brokenaway, of a vat containing a: support for the wood pulp sheets to be nitrated.

Fig. 2 is a perspective view of another device for maintaining the sheets a few millimeters apart in the bath.

Fig. 3 shows diagrammatically an apparatus for carrying out the process according to the present invention.

The wood pulp sheets suitable for the manufacture are those which are found -in commerce in the well-known form of thick sheets similar to blotting paper and used in the manufacture of viscose. These sheets, of the size current in trade, are, irst, placed in grooves of a support constructed of acid proof metal, such as aluminum, and capable of being immersed withits contents in a vat filled with acids'which compose the nitration bath. v

The grooves of the support, which is similar to that used for the vertical washing of photographic plates, are brought sufficiently close to one another to leave between the sheets a space of a few millimeters only. A.

support of this character is illustrated in Fig. 1, and is generally designated l, the grooves or seats :2 being formed in its upper and lower horizontal members 3 and 4. The pulp sheets are designated 5 and the vat is designated 6.

The sheets of pulp may alternatively be perforated at selected points of their surface as indicated at 7 in Fig.- 2, and be placed in juxtaposition,- strung one after another on glass rods8 so that they may be separat/ed bysmall spaces, as shown.

The unit made up in one or the other of vthe two Ways mentioned may consist of any number of sheets-for instance, 50 sheets weighing 100 grams eachand the nitration is elfected afterwards simultaneously inthe same vat on several units of this description, say 6 for example, representing 30 kilograms of pulp which after nitraftion will yield, on an average, 5() kilograms of nitrocellulose.

The immersion vats 6 may be made of any resist-ing metal but, as it is 'most important, from a hygienic point of View, to operate in closed vessels and therefore to carry out the first washing operations in the actual vat Where the nitration takes place, preference is given to aluminum which is very resistant to acids either concentrated or diluted with water. The shape and dimensions of these vats may vary, as may also the method of suspending the sheets.

By way of example, a construction suitable for industrial manufacturing is represented in Fig. 3 which shows a rectangular vat A surrounded by a jacket B, through which a current of water at a constant tempera'ture is continuously circulating, the vat having its top part closed by a light and close-fitting cover C of the same metal.

When said vat is empty and the cover raised, the free ends of the rods carrying the units are deposited on cross bars D D, the cover is fitted on, and the different valves with which the vat is externally provided.

permit the nitration and the first washings being carried out hermetically, For this purpose, the Valve El which regulates the iniux of the nitrifying mixturel supplied by the upper tank F, is opened. The liquid rises from the bottom of the vat and Iills it to the level necessary to entirely immerse the pulp sheets; such levelbeing reached when it is observed from outside that the intermediate` funnel G begins to be filled. At

that moment valve E is closed and the nitra tion proceeds.

During nitration, the circulation of the Water is maintained in the jacket B. The temperature of the refrigerating Water should only vary Within very narrow limits (l or 2 degrees, for instance); it must not appreciably exceed 15 C. This condition, which is indispensable to insure tl'ie success of the operation, is easily realized by employing an intermediate vat in which the spring and Well water etc., used may he cooled by a circulation of brine obtained from any refrigerating apparatus.

The nitration is thus carried on at a constant temperature Without any need to raise the cover ot' the vat, but its duration cannot be predetermined because it depends upon the composition and temperature of the ni tration bath employed.

lt is known that the nitrocellulose ohtained has a substantially-constant percentage ot' nitrogen'when the bath used is itself constant. This is Why, in order to prepare the variety of soluble nitrocellulose called collodion quality with 10 'or 10.5% of nitrogen, the nitration bath must, for instance, contain:

mso. 62% rinos 20% ngo 18% If a bath oi this description is used, the total nitration of the Wood pulp will require about 12 hours if theoperation is carried on at a temperature of 15C., and about 2() hours at lO-ll".

With these temperatures, the nitration proceeds gradually and smoothly. lt may be checked by testin specimen sheets taken, say, every hour. T e percentage of nitrogen and the increase in Weight of said sheets may be expressed by curves. Such curves are regular and at the `end of the period above-mentioned they become asymptotic, showing that the maximum of nitration has been reached.

A. longer treatment, even extending to many hours, does not appreciably alter either the percentage of nitrogen or the Weight of the nitrated product.

Unlike the violent reactions occurring in nitration in drying machines, a considerable margin of time remains available Which makes it possible to Work steadily and to carry out, if necessary, in the course of working any test considered necessary.

Such margin of time is greater, as the bath is colder. But it is advisable not to pro long the period of nitration unreasonably and to x a maximum period of 24 hours, and for this ,purpose to maintain the requisite temperature of the refrigeration water.

The use of acid mixtures of suitable composition makes it possible to obtain from the Wood pulp other varieties ofnitrocellulose With the same facility as the collodion quality, including explosives containing,r 13% ot' nitrogen. The quantities yielded do nul. appreciably differ from those obtained With cotton.

lo the initial tank F to serve for a further i operation.

When the vat is empty, about half an hour is allowed to elapse to permit t-he sheets of nitrated pulp to completely drain oil', valve .L is vthen closed and the Washing is started. 'l`he washing Water is supplied through the pipe O controlled' by the valve l), fills up the tank, meets the overiow R and runs over into the drain pipe. This lixiviation is carried on until the evacuated Water shows no appreciable acidity. The Washing is stopped by closing the valve l and the vat is emptied by opening the valve S. y

The nitration operation is then completed. The cover C is removed and the parcels of sheets are Withdrawn either with their grooved supports or With the aid of the glass rods upon which said sheets are suspended. The vat thus emptied may at once be used again for a fresh operation.

The nitrated sheets are then. transported to the finishing workshop and placed, as sembled together as they are, in wooden tanks or vats of a large size for the purpose of being therein stabilized, modified (as regards the viscosity of the solutions they areI to supply afterwards), bleached and thoroughly re-Washed, being immersed vertically in the various baths in the same way as during nitration.

The Wonderful consistency of the sheets of nitrated Woodpulp enables them to stand avery long contact even with boiling baths. They are very easily manipulated with their supports up to the final drying which is ef- :tected either in a stove in vacuo or in any suitable dryer. After drying, the sheets are finally removed from their supports, cut and packed in any dimensions as in the case of ordinary cardboard.

If it is desired to keep the sheets in a moist condition, they are arranged in regular piles which are subjected to the action of a press for the purpose o squeezing out of themr the'water in excess before packing them. The moist sheets may also be reduced to small fragments by subjecting them to the rapid action of known rotary Crushers, which at once transform them luto a light pulp. t

As has already been. stated, the process -ous and unhealthy use of ntration dryin machines and requires neither heaters wit acids, -circulation piles nor dehydration turbines.

The sheets of wood pulp immersed in any liquid retain after drainln very little of this liquid as compared' witli absorbed b cotton under the same circumstances. T is is why special dr ing may be done away with and replace by simple draining carried out, in the case of acids, in closed vessels.

price ofthe raw material.

I claim as my invention 1. A process for manufacturing nitrated cellulose from wood pulp, comprising the steps of immersing thick wood-pulp sheets of low porosity in a nitration bath the temperature of wh'ch is below 15 C. but not less than 5 C., and maintaining said bath at a constant temperature during the whole period of nitration, such period var ing according to the temperature of the ath.

the quantities To these advantages are added the low 2. A process for manufacturing nitrated cellulose from wood pulp, comprising the ste s of immersing thickJ wood-pulp sheets of ow porosity in a nitration bath the temperature of which is below 15 C. but not less than 5 C.; maintaining said sheets entirely free from contact` with one another during their sta within the bath so as to y enable the bath liquid to have free and uninterrupted access to all parts of them; andl maintaining the bath itself at a constant temperature during the whole period of nitration, such period varying according to the temperature of the bath. v

3. A process for manufacturing nitrated cellulose from wood pulp, comprisin the steps of immersing thick wood-pulp s eets of low porosity in a nitrationl bath contained in a closed vessel, the temperature of such bath being below' 15 C. but'not less than 5 C.; maintaining said bath at a constant temperature during the Whole period of nitration, such period varying according to the temperature of the bath; evacuating the bath liquid from said vessel at the conclusion of nitration, and leaving the nitrated sheets therein-to drain; and then washing the drained sheets in said vessel with water. whereof I have signed this In witness specification.

VICTOR PLANCHON. 

